RFC 2208 RSVP Applicability and Deployment September 19971. Introduction
RSVP [RFC 2205] is a unicast and multicast signalling protocol,
designed to install and maintain reservation state information at
each router along the path of a stream of data. The state handled by
RSVP is defined by services [RFC 2211] and [RFC 2212] specified by
the Integrated Services WG. These services and RSVP are being
introduced to the IETF's standards track jointly. From henceforth,
the acronym RSVP on its own is used as a shorthand for the signalling
protocol combined with the integrated service specifications.
RSVP must be used in conjunction with several additional components,
described in Table 1.
Table 1 Additional Components of Resource Reservation
1. Message formats in which parameters for desired services can be
expressed. A proposed standard set of these formats is specified
in [RFC 2210].
2. Router and host mechanisms (e.g. packet classification and
scheduling, admission control algorithms) to implement one or
both of the models [RFC 2211] and [RFC 2212], which are also
in the standards track.
3. Message formats in which parameters for desired policies for
admission control and resource use can be expressed. A small
common subset of these formats for standards track is in the
RSVP WG's charter. The Policy objects in the RSVP Protocol
Specification are optional only at this time.
4. Diversely located mechanisms implementing desired admission
control policy functions, including authorization and other
security mechanisms.
In the presence of some form of each component in Table 1, RSVP-
enabled applications can achieve differentiated qualities of service
across IP networks. Networked multimedia applications, many of which
require (or will benefit from) a predictable end-user experience, are
likely to be initial users of RSVP-signalled services.
Because RSVP and the integrated services and other components listed
in Table 1 mark a significant change to the service model of IP
networks, RSVP has received considerable interest and press in
advance of its release as a standards track RFC. At present, many
vendors of operating systems and routers are incorporating RSVP and
integrated services into their products for near-future availability.
The goal of this applicability statement is to describe those uses of
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RFC 2208 RSVP Applicability and Deployment September 1997
the current RSVP specification that are known to be feasible, and to
identify areas of limitation and ongoing chartered work addressing
some of these limitations.
2. Issues Affecting Deployment of RSVP
Wide scale deployment of RSVP must be approached with care, as there
remains a number of outstanding issues that may affect the success of
deployment.
2.1. Scalability
The resource requirements (processing and storage) for running RSVP
on a router increase proportionally with the number of separate
sessions (i.e., RSVP reservations). Thus, supporting numerous small
reservations on a high-bandwidth link may easily overly tax the
routers and is inadvisable. Furthermore, implementing the packet
classification and scheduling capabilities currently used to provide
differentiated services for reserved flows may be very difficult for
some router products or on some of their high-speed interfaces (e.g.
OC-3 and above).
These scaling issues imply that it will generally not be appropriate
to deploy RSVP on high-bandwidth backbones at the present time.
Looking forward, the operators of such backbones will probably not
choose to naively implement RSVP for each separate stream. Rather,
techniques are being developed that will, at the "edge" of the
backbone, aggregate together the streams that require special
treatment. Within the backbone, various less costly approaches would
then be used to set aside resources for the aggregate as a whole, as
a way of meeting end-to-end requirements of individual flows.
In the near term, various vendors are likely to use diverse
approaches to the aggregation of reservations. There is not
currently chartered work in the IETF for development of standards in
this space. A BOF, Future Directions of Differential Services, on
April 7, 1997, at the Memphis IETF, is to consider the IETF's next
steps on this, among other issues. Public documentation of
aggregation techniques and experience is encouraged.
2.2. Security Considerations
The RSVP WG submission for Proposed Standard includes two security-
related documents [Baker96, RFC 2207]. [Baker96] addresses denial and
hijacking or theft of service attacks. [RFC 2207] addresses RSVP
mechanisms for data flows that themselves use IPSEC.
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RFC 2208 RSVP Applicability and Deployment September 1997
The first document is proposed to protect against spoofed reservation
requests arriving at RSVP routers; such requests might be used to
obtain service to unauthorized parties or to lock up network
resources in a denial of service attack. Modified and spoofed
reservation requests are detected by use of hop-by-hop MD5 checksums
(in an Integrity Object) between RSVP neighbor routers. As
described, RSVP hop-by-hop authentication assumes that key management
and distribution for routers is resolved and deployed. Until an
effective key infrastructure is in place, manually keyed session
integrity might be used. In addition, [Baker96] may be updated with
RFC 2085.
That RSVP needs an effective key infrastructure among routers is not
unique to RSVP: it is widely acknowledged that there are numerous
denial of service attacks on the routing infrastructure (quite
independent of RSVP) that will only be resolved by deployment of a
key infrastructure.
Theft of service risks will require the user to deploy with caution.
An elementary precaution is to configure management logging of new
and changed filter specifications in RSVP-enabled infrastructure,
e.g. the newFlow trap [RFC 2206].
The Integrity object defined by [Baker96] may also play a role in
policy control, as will be described in 2.3.
The second security-related document provides a mechanism for
carrying flows in which the transport and user octets have been
encrypted (RFC 1827). Although such encryption is highly beneficial
to certain applications, it is not relevant to the functional
security of RSVP or reservations.
The following section on Policy Control includes additional
discussion of RSVP authorization security.
2.3. Policy Control
Policy control addresses the issue of who can, or cannot, make
reservations once a reservation protocol can be used to set up
unequal services.
Currently, the RSVP specification defines a mechanism for
transporting policy information along with reservations. However,
the specification does not define policies themselves. At present,
vendors have stated that they will use the RSVP-defined mechanism to
implement proprietary policies.
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RFC 2208 RSVP Applicability and Deployment September 1997
The RSVP WG is chartered to specify a simple standardized policy
object and complete simple mechanisms for session use of the
Integrity object in the near future. This applicability statement
may be updated at the completion of the WG's charter.
Before any decision to deploy RSVP, it would be wise to ensure that
the policy control available from a vendor is adequate for the
intended usage. In addition to the lack of documented policy
mechanisms in any of the policy areas (such as access control,
authorization, and accounting), the community has little experience
with describing, setting and controlling policies that limit Internet
service. Therefore it is likely that vendor solutions will be
revised often, particularly before the IETF has developed any policy
specification.
3. Recommendations
Given the current form of the RSVP specifications, multimedia
applications to be run within an intranet are likely to be the first
to benefit from RSVP. SNA/DLSW is another "application" considered
likely to benefit. Within the single or small number of related
administrative domains of an intranet, scalability, security and
access policy will be more manageable than in the global Internet,
and risk will be more controllable. Use of RSVP and supporting
components for small numbers of flows within a single Internet
Service Provider is similar to an intranet use.
Current experience with RSVP has been collected only from test runs
in limited testbeds and intranet deployment. We recommend that
people begin to use RSVP in production intranet or limited ISP
environments (as mentioned above), in which benefits can be realized
without having to resolve some of the issues described in Section 2.
To quote RFC 2026 about the use of Proposed Standard technology:
Implementors should treat Proposed Standards as immature
specifications. It is desirable to implement them in order to gain
experience and to validate, test, and clarify the specification.
However, since the content of Proposed Standards may be changed if
problems are found or better solutions are identified, deploying
implementations of such standards into a disruption-sensitive
environment is not recommended.
General issues of scalability, security and policy control as
outlined in Section 2 are the subjects of active research and
development, as are a number of topics beyond this applicability
statement, such as third-party setup of either reservations or
differentiated service.
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